As lighter, smaller portable electronic devices with increasing functionality are developed, there is generally a corresponding increasing demand for smaller, lighter batteries with increased energy density to power the devices. Such batteries can be used in commercial applications, such as portable notebooks and computers, digital and cellular phones, personal digital assistants, and the like, and higher energy applications, such as hybrid and electric cars, and military or defense applications.
Lithium sulfur batteries have been developed to address some of these concerns. Lithium sulfur batteries are rechargeable, have a relatively high energy density and specific power, are relatively light, can operate over a wide temperature range (about −50° C. to about 70° C.), use relatively inexpensive cathode materials (sulfur), and are relatively safe for the environment, compared to other battery technologies such as nickel metal hydride (NiMH), lithium ion, nickel cadmium (Ni—Cd), and lead acid batteries.
Lithium sulfur batteries generally include a lithium anode, an electrolyte, a porous separator, and a sulfur cathode. In a discharge operation of the battery, the lithium anode is oxidized to form lithium ions, while the sulfur cathode is reduced to form polysulfides, which are soluble products. During a charging operation, polysulfides are oxidized to form solid sulfur.
Unfortunately, with conventional lithium-sulfur batteries, the sulfur cathode discharge products, polysulfides, may migrate through the separator and react on a surface of the anode, causing further performance and capacity degradation.
Various attempts have been made to address these issues with conventional lithium-sulfur batteries. One technique includes modifying the electrolyte to attempt to provide additional sulfur for the electrochemical reaction, and another technique includes providing a protective sheath around the anode. Neither approach has been completely successful. Modified electrolyte solutions fail to completely control polysulfide solubility, and protective lithium anode layers have other undesirable effects on the electrochemical characteristics of the battery. Accordingly, improved lithium-sulfur batteries and components thereof are desired.